Pros:

Minecraft.
Extracted from the original deathcraft 2 campaign for peoples enjoyment, thus rendering the normal minecraft zombies unneeded unless some people like that more.

Cons:

This may or may not be compatible with the l4d1 campaigns in l4d2. Like the patients in no mercy.

Conclusion:

I feel that this has replaced the Minecraft Zombies addon, so I think that he should've replaced that with this.